1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for causing a recording head to discharge an ink to a recording medium to perform recording, and a temperature control method therefor.
2. Related Background Art
A recording apparatus such as a printer, a copying machine, a facsimile apparatus, or the like records an image consisting of a dot pattern on a recording medium such as a paper sheet or a plastic thin plate.
The recording apparatus can be classified as an ink-jet type, wire dot type, thermal type, laser-beam type, and the like according to a recording method. Of these apparatuses, in the ink-jet type apparatus (ink-jet recording apparatus), an ink droplet (recording liquid) is discharged from a discharge port of a recording head, and is attached to a recording medium, thereby performing recording.
In recent years, a large number of recording apparatuses have been used, and are required to have a high recording speed, a high resolution, high image quality, and low noise.
As a recording apparatus which satisfies these requirements, the ink-jet recording apparatus is known.
In the ink-jet recording apparatus, since recording is performed by discharging an ink from a recording head, the apparatus is considerably influenced by the temperature of the recording head.
For this reason, a conventional ink-jet recording apparatus employs a so-called closed-loop control method wherein a temperature sensor and a temperature control heater which increase cost are arranged in a recording head unit, so that the temperature of the recording head is controlled to fall within a desired range on the basis of the detected temperature of the recording head. As the temperature control heater, a heating member joined to a recording head unit or a discharge heater in a bubble-jet recording apparatus, proposed by CANON INC., for discharging an ink droplet by growing bubbles by film boiling of an ink is used. When the discharge heater is used, it must be energized so as not to generate bubbles.
In particular, in a bubble-jet recording apparatus (which is proposed by CANON INC., and forms bubbles in a solid or liquid ink using a heat energy to obtain an ink droplet to be discharged), since its discharge characteristics are largely varied depending on the temperature of the recording head, as is conventionally known, closed-loop temperature control tends to be performed. Alternatively, only an inexpensive printer which is used for a compact electronic calculator which disregards printing quality, density nonuniformity, and the like is available.
However, in recent years, since portable OA equipments such as laptop personal computers have become popular, portable printers are required to have high quality. A disposable cartridge type printer in which a head and an ink tank are integrated will lead the portable printers since it has a compact structure. In addition, the disposable cartridge type printer will become more popular in terms of maintenance due to an increase in popularity of home- or personal-use wordprocessors, personal computers, and facsimile apparatuses.
In this case, since the temperature sensor and the heater for temperature control are incorporated in the disposable cartridge, the following drawbacks are posed.
(1) Variation in temperature measurement values due to variation in temperature sensor
Since a disposable head is an expendable supply, a sensor having a variation in characteristics is connected to the printer main body every time the head is exchanged.
In a bubble-jet recording head, since a discharge heater is manufactured in a semiconductor process, a diode sensor for detecting a temperature of a recording head must be integrally formed in a single process to decrease cost. Since the diode sensor suffers from a variation in the manufacture, it does not have high precision like in a temperature sensor as a selected product, and may often cause a difference of 15.degree. C. or more among manufacturing lots as measurement values of an ambient temperature.
For this reason, closed-loop control using the temperature sensor of the recording head requires a complicated adjustment operation for adjusting a variation in temperature sensor of the recording head in an adjustment process, or mounting a temperature sensor which is measured and ranked in a main body, and correcting it using an adjustment selection switch.
These operations considerably increase manufacturing cost, and impair operability. An increase in signal processing volume caused by these operations, and a considerable increase in processing volume of an MPU caused by closed-loop control itself exert a heavy load on design of a compact or portable printer main body apparatus.
(2) Countermeasure against electrostatic noise
Since a disposable head is an expendable supply, a user frequently attaches or detaches it to or from a main body. For this reason, contacts of the main body are always exposed.
Since the output from the temperature sensor is directly supplied to a circuit on a printed circuit board of the main body through a carriage and a flexible wiring, a temperature measurement circuit is very susceptible to electrostatic noise. Since a compact or portable printer cannot have a sufficient shield effect in its housing, it is further weak against electrostatic noise.
Therefore, in a conventional temperature detection method, an electrostatic shield, and parts as a countermeasure against electrostatic noise must be added at respective portions for only a single temperature sensor, thus considerably disturbing a compact structure, a decrease in cost, and high image quality.